PHYSICOCHEMICAL PROPERTIES OF THE FLUOROQUINOLONE ANTIMICROBIALS .3. COMPLEXATION OF LOMEFLOXACIN WITH VARIOUS METAL-IONS AND THE EFFECT OF METAL-ION COMPLEXATION ON AQUEOUS SOLUBILITY

The complexation of lomefloxacin with five metal ions (Al3+, Ca2+, Mg2+, Bi3+, and Fe3+)commonly found in antacid or vitamin preparations has been studied at 25-degrees-C. The stability constants and stoichiometries were determined by measuring the change of aqueous solubility of lomefloxacin as a function of metal ion concentration. The concentration of lomefloxacin was determined by liquid chromatography. The stoichiomtery of binding was confirmed independently by FAB-MS analysis of aqueous solutions of the complexes. The binding constants were dependent on the nature of the metal ion and were related to the charge density. The pharmaceutical and biopharmaceutical implications of the effects of metal ion complexation on the aqueous solubility of lomefloxacin are discussed.